TOnfc, 05 



influence of a low-pressure or cyclonic system 

 the velocity of its movement is very much ac- 

 celerated until it has moved into the zone of 

 quiet air in the center, where it is ascending. 



In the upper regions of the atmosphere 

 there are counter currents flowing in the oppo- 

 site direction. The downward flow at the area 

 of high pressure compresses the air near the 

 surface of the earth and rarefies it in the 

 higher regions of the atmosphere, while the 

 opposite effect is going on over the center of 

 low pressure, the air being rarefied nearer the 

 surface of the earth, but condensed above nor- 

 mal in the higher regions by the upward cur- 

 rent, which causes an overflow back toward the 

 rarefied upper regions over the area of high 

 pressure. 



It will be observed that the ordinary storm 

 has a compound motion. The whole system 

 moves in an easterly direction, while the winds 

 are blowing spirally about the storm center. 

 If we should be in the track of a moving storm 

 so that its center passed over us the winds at 

 the beginning would blow in one direction and 

 then there would come a subsidence until it 

 had moved forward through the quiet zone, 

 when we should feel the wind in the opposite 

 direction until the area of low pressure had 

 moved forward into the region of high pres- 

 sure. The velocity of the wind will be deter- 

 mined by the difference of pressure between 



